Gearbox for vehicles

ABSTRACT

A gearbox for vehicles that includes a split gearbox, a main gearbox and a range gearbox, which is shiftable into a low range gear position and a high range gear position. The range gearbox includes a planetary gear with a ring gear wheel, a sun gear wheel and a planet carrier, on which at least one planet gear wheel is rotatably mounted. A gearbox housing surrounds the planetary gear. A first axially movable coupling sleeve engages the planet carrier with the gearbox housing. A second axially movable coupling sleeve engages the ring gear wheel with an output shaft to shift into a reverse gear. A crawler gear in the main gearbox is arranged to transfer torque through the gearbox when the range gearbox is shifted into the reverse gear.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. § 371 national phase conversionof PCT/SE2018/050069, filed Jan. 31, 2018, which claims priority ofSwedish Patent Application No. 1750109-9, filed Feb. 8, 2017, thecontents of all of which are incorporated herein by reference. The PCTInternational Application was published in the English language.

FIELD OF THE INVENTION

The present invention relates to a gearbox for vehicles and to a vehiclecomprising such a gearbox according to the appended claims.

BACKGROUND AND PRIOR ART

In vehicles, and especially for heavier vehicles such as trucks, thegearbox comprises a main gearbox and often also a range gearbox, whichis connected to the main gearbox. The range gearbox doubles the numberof gears in the gearbox. The range gearbox usually includes a planetarygear, which has a low gear and a high gear, so that the gearbox can bedivided into a low range gear position and a high range gear position.In the low range gear position, a downshift takes place through theplanetary gear, and, in the high range gear position, the gear ratio is1:1 in the planetary gear.

The range gearbox is usually provided between the main gearbox and apropeller shaft coupled to the drive wheels of the vehicle. The rangegearbox is accommodated in a gearbox housing and comprises an inputshaft coupled to the main gearbox, an output shaft, and the planetarygear, which is disposed between the input shaft and the output shaft.The planetary gear usually comprises three components, which arerotatably arranged relative to each other. The three components are asun gear wheel, a planet carrier with planet gear wheels and a ring gearwheel. With knowledge of the number of teeth of the sun gear wheel andthe ring gear wheel, the relative speed of the three components can bedetermined during operation. In a range gearbox, the sun gear wheel canbe rotatably connected to the input shaft, a number of planet gearwheels, which engage the sun gear wheel, and are rotatably mounted onthe planet carrier, which is fixedly connected to the output shaft, andan axially displaceable ring gear wheel, which surrounds and engages theplanet gear wheels.

In a known range gearbox, the low range gear position and the high rangegear position are obtained by displacing the ring gear wheel axiallybetween the low range gear position, in which the ring gear wheel isrotationally locked relative to the gearbox housing, and the high rangegear position, in which the ring gear wheel is rotatable relative to thegearbox housing and where the ring gear wheel, the planet gear wheelsand the sun gear wheel rotate as a common unity. The known planetarygear comprises two coupling rings on each side of the ring gear wheeland two synchronizing rings arranged on each side of the ring gearwheel.

The document WO0155620 discloses a synchronization device in a planetarygear in a range gearbox. The planetary gear includes a sun gear wheel, aplanet carrier and a ring gear wheel. The sun gear wheel is rotatablyconnected with the input shaft and a number of planet gear wheelsengaging with the sun gear wheel, which planet gear wheels are rotatablymounted on the planet carrier, which is connected to the output shaft.An axially displaceable ring gear wheel surrounds and meshes with theplanet gear wheels. Low and high gears are obtained by displacing thering gear wheel axially between a low range gear position and a highrange gear position.

However, there are range gearboxes in which the synchronization devicesare replaced with coupling sleeves provided with splines. By controllingthe transmission to synchronous speed between the two components to beassembled, an axial displacement of the coupling sleeve along the twocomponents is made possible in order to connect them. When thecomponents should be detached, the transmission is controlled so thattorque balance occurs between the components so that the coupling sleeveis not transmitting torque. It then becomes possible to move thecoupling sleeve along the components in order to disengage them fromeach other.

The document U.S. Pat. No. 6,196,944 shows a planetary gear comprising asun gear wheel, a planet carrier with planet gear wheels and a ring gearwheel. The sun gear wheel may be connected to the input shaft by meansof a coupling sleeve in a low range gear position and disengaged fromthe input shaft in a high range gear position. In the high range gearposition, the input shaft is connected to the planet carrier by means ofthe same coupling sleeve. The ring gear wheel is firmly connected to agearbox housing. The known planetary gear is arranged in an auxiliarygearbox, having only two gear positions.

The reverse gear in a transmission in a vehicle is often arranged in themain gearbox, which then comprises a gear that is engaged when thevehicle is to be driven in the reversed direction. The gear wheels,which are intended for the reverse gear, cause an elongation of the maingearbox, and an undesired increase in weight of the vehicle.

The document WO2015/183153A1 shows a gearbox for vehicles comprising arange gearbox provided with a first, a second and a third axiallymovable coupling sleeves acting on a planetary gear in the rangegearbox. Depending on the axial position of the coupling sleeves, areverse gear in the gearbox may be achieved.

The range gearbox must have a diameter, a length and a weight withinreasonable limits. If the diameter of the planetary gear in the rangegearbox is too large, the gearbox will not fit in a vehicle due togeometrical and design limits of the vehicle. An increased diameter ofthe planetary gear in the range gearbox also results in an increasedweight, which results in an increased overall weight of the vehicle.This may lead to an increase in the fuel consumption of the vehicle.

When the planetary gear in the range gearbox is designed with a limiteddiameter, the gear ratio in the range gearbox will be limited to acertain amount. This may affect the driveability of the vehicle in thereverse direction since of the vehicle may not be driven with a velocitylow enough in the reverse direction when a clutch between an engine andthe gearbox is completely engaged.

Since the gearbox must transmit a considerable amount of torque, thegear ratio may not be increased by minimizing the diameter of the sungear wheel. If the sun gear wheel has a very small diameter, it may notwithstand the considerable amount of torque needed. In addition, byusing a small sun gear wheel, the diameter of the planet gear wheels mayget into physical contact with each other due to an increased diameterof the planet gear wheels.

SUMMARY OF THE INVENTION

There is a need for a gearbox provided with a reverse gear in a rangegearbox. There is also a need for a gearbox, which exhibits smalldimensions relative to the possible transmission of torque. There isalso a need for a gearbox where all components in the gearbox areutilized effectively so that low energy is required when shifting. Inaddition, there is a need for a gearbox, which brings the overallcomponents in the gearbox to a minimum in order to save manufacturingand repair costs.

The object of the present invention is therefore to further develop agearbox provided with a reverse gear in a range gearbox.

A further object of the invention is to provide a gearbox, having smalldimensions in relation to possible transmission of torque.

Another object of the present invention is to provide a gearbox, whichbrings the overall components in the gearbox to a minimum in order tosave manufacturing and repair costs.

A further object of the invention is to provide a gearbox that utilizesall of the transmission components effectively.

A further object of the present invention is to provide a gearbox whichrequires low energy for shifting.

These objects are achieved with the above-mentioned gearbox according tothe appended claims.

According to an aspect of the invention, a gearbox for vehicles isprovided. The gearbox comprises a split gearbox, a main gearbox and arange gearbox, which is shiftable into a low range gear position and ahigh range gear position. The range gearbox comprises a planetary gearwith a ring gear wheel, a sun gear wheel and a planet carrier, on whichat least one planet gear wheel is rotatably mounted. The ring gear wheeland the sun gear wheel engage with the at least one planet gear wheel. Agearbox housing surrounds the planetary gear. A first axially movablecoupling sleeve is arranged to engage the planet carrier with thegearbox housing, and a second axially movable coupling sleeve isarranged to engage the ring gear wheel with an output shaft for shiftinginto a reverse gear in the gearbox. A crawler gear in the main gearboxis arranged to transfer torque through the gearbox when the rangegearbox is shifted into the reverse gear.

The vehicle may be driven in the reverse direction when the planetarygear in the range gearbox is shifted into the reverse gear. Thearrangement of a crawler gear for the transfer of torque through thegearbox, when the range gearbox is shifted into the reverse gear,facilitates the vehicle to be driven in the reverse direction at avelocity, which is low enough for the driver of the vehicle to havecontrol over the vehicle even when a clutch between an engine and thegearbox is completely engaged. The gear ratio of the crawler gearresults in that the range gearbox may have a limited diameter and whilethe driveability of the vehicle in the reverse direction is notadversely affected. A limited diameter of the range gearbox will bringthe overall components in the gearbox to a minimum, and thusmanufacturing and repair costs will be saved. The sun gear wheel in theplanetary gear may be provided with a diameter, which withstands theconsiderable amount of torque needed. Thus, there is no need to increasethe gear ratio of the planetary gear in the range gearbox by minimizingthe diameter of the sun gear wheel.

According to a further aspect of the invention, the gear ratio of thecrawler gear is in the range 3.1:1=3.9:1. When the gear ratio of thecrawler gear is in the range 3.1:1-3.9:1, the vehicle may be driven inthe reverse direction in a velocity, which is low enough to have controlover the vehicle. Thus, the driveability of the vehicle in the reversedirection will be acceptable. The overall dimensions of the gearbox canbe reduced. In addition, there is no need to increase the gear ratio ofthe planetary gear in the range gearbox by minimizing the diameter ofthe sun gear wheel.

According to a further aspect of the invention, the gear ratio of thecrawler gear is in the range 3.4:1-3.6:1. When the gear ratio of thecrawler gear is in the range 3.4:1-3.6:1, the vehicle may be driven inthe reverse direction in a velocity, which is low enough to have controlover the vehicle. Thus, the driveability of the vehicle in the reversedirection will be improved. The overall dimensions of the gearbox can bereduced further. In addition, there is no need to increase the gearratio of the planetary gear in the range gearbox by minimizing thediameter of the sun gear wheel.

According to a further aspect of the invention, the crawler gear is onlyengaged when the gearbox is shifted into the reverse gear, and also inthe forward direction when the range gearbox is shifted into the lowrange position, but not in the high range position. In comparison toother gears used when driving a vehicle in the forward direction, thereverse gear is less used and also the crawler gear in the forwarddirection is less used. In addition, the torque transferred through thecrawler gear is less than the torque transferred through other gears inthe gearbox due to the high gear ratio in the crawler gear. For thisreason, a limited wear of the crawler gear can be expected. Therefore,the crawler gear may be designed for bringing the overall dimensions ofthe gearbox to a minimum.

According to a further aspect of the invention, the planetary gear isarranged to have a gear ratio in the range 3.1:1-3.9:1 when shifted intothe reverse gear. When the gear ratio of the planetary gear is in therange 3.1:1-3.9:1, the vehicle may be driven in the reverse direction ata velocity, which is low enough to have control over the vehicle. Thus,the driveability of the vehicle in the reverse direction will beacceptable. The overall dimensions of the gearbox can be reduced. Also,there is no need to increase the gear ratio of the planetary gear in therange gearbox by minimizing the diameter of the sun gear wheel.

According to a further aspect of the invention, the planetary gear isarranged to have a gear ratio in the range 3.3:1-3.6:1 when shifted intothe reverse gear. When the gear ratio of the planetary gear is in therange 3.3:1-3.6:1, the vehicle may be driven in the reverse direction ata velocity, which is low enough to have control over the vehicle. Thus,the driveability of the vehicle in the reverse direction will beimproved. The overall dimensions of the gearbox can be reduced further.In addition, there is no need to increase the gear ratio of theplanetary gear in the range gearbox by minimizing the diameter of thesun gear wheel.

According to a further aspect of the invention, the split gearbox andthe main gearbox are together arranged to have a largest gear ratio,which is larger than the gear ratio of the planetary gear in the rangegearbox when shifted into the reverse gear. This results in that thesplit gearbox and the main gearbox together will have a large ratiospread. This way, the vehicle may be driven in the reverse direction ata velocity, which is low enough to have control over the vehicle. Thus,the driveability of the vehicle in the reverse direction will be verygood. The overall dimensions of the gearbox can be reduced and there isno need to increase the gear ratio of the planetary gear in the rangegearbox by minimizing the diameter of the sun gear wheel. The definitionof the ratio spread is the largest common gear ratio of the splitgearbox and the main gearbox divided with the minimum common gear ratioof the split gearbox and the main gearbox.

According to a further aspect of the invention, the width of a crawlergear wheel of the crawler gear is smaller than the width of a gear wheelin a gear in the main gearbox having the second largest gear ratio. Incomparison to gears used when driving a vehicle in the forwarddirection, the reverse gear and the crawler gear are less used. Inaddition, the torque transferred through the crawler gear is less thanthe torque transferred through other gears in the gearbox due to thehigh gear ratio in the crawler gear. For this reason, a limited wear ofthe crawler gear can be expected. Thus, the crawler gear may be designedwith a width that is smaller than the width of a gear wheel in a gear inthe main gearbox having the second largest gear ratio, because the wearof the crawler gear may be limited. This may also reduce the length ofthe gearbox.

According to a further aspect of the invention, one crawler gear wheelof the crawler gear is arranged on a mainshaft in the main gearbox andthe another crawler gear wheel of the crawler gear is arranged on alayshaft. This way, torque may be transferred through the crawler gearin the gearbox.

According to a further aspect of the invention, the gearbox is arrangedto have an overlapping gear ratio in at least the highest gear in thelow range gear position and at least the lowest gear in a high rangegear position. The overlapping gear ratio will increase the ratio spreadin the gearbox. Such a gearbox brings the overall components in thegearbox to a minimum and utilizes all of the transmission componentseffectively.

According to a further aspect of the invention, the gearbox is arrangedto have an overlapping gear ratio in the two highest gear in the lowrange gear position and the two lowest gear in a high range gearposition. The overlapping gear ratio in the two highest gears in the lowrange gear position and the two lowest gears in a high range gearposition will increase the ratio spread in the gearbox. This way, thevehicle may be driven in the reverse direction in a low enough velocityto have control over the vehicle. The driveability of the vehicle in thereverse direction will be very good. Such a gearbox brings the overallcomponents in the gearbox to a minimum and utilizes all of thetransmission components effectively.

The above-mentioned objects are also achieved by a vehicle, includingthe above-mentioned gearbox, according to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Below is a description of, as examples, preferred embodiments of theinvention with reference to the enclosed drawings, in which:

FIG. 1 shows schematically a side view of a vehicle with a gearboxaccording to the invention,

FIG. 2 shows schematically a cross section of the main gearbox and asplit gearbox according to the invention,

FIG. 3 shows schematically a cross section of the gearbox according tothe invention in a low range gear position,

FIG. 4 shows schematically a cross section of the gearbox according tothe invention in a high range gear position, and

FIG. 5 shows schematically a cross section of the gearbox according tothe invention in a reverse position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows schematically a side view of a vehicle 1, provided with apowertrain 3, which comprises a gearbox 2 according to the invention.The powertrain 3 also comprises an internal combustion engine 4, apropeller shaft 10 and drive wheels 8. The drive wheels 8 are coupled tothe gearbox 2 via the propeller shaft 10. The gearbox 2 comprises arange gearbox 15B, which aims to double the number of gearopportunities. The gearbox 2 is surrounded by a gearbox housing 12.

FIG. 2 shows a schematic sectional view of a gearbox 2 according to thepresent invention. The gearbox 2 comprises a main gearbox 15A, a splitgearbox 15C and the range gearbox 15B. The range gearbox 15B isshiftable into a low range gear position, a high range gear position anda reverse gear position, which will be explained in more detail below.The vehicle 1 may be driven in the reverse direction when the rangegearbox 15B is shifted into the reverse gear. The largest gear ratio inthe split gearbox 15C and the main gearbox 15A together may be largerthan the gear ratio in a planetary gear 14 (FIG. 3) in the range gearbox15B, when the planetary gear 14 is shifted into the reverse gear. Thesplit gearbox 15C and the main gearbox 15A may together be arranged tohave a largest gear ratio over 4:1 and the planetary gear 14 in therange gearbox 15B may be arranged to have a gear ratio less than 4:1when shifted into the reverse gear. With such a common gear ratio in thesplit gearbox 15C and the main gearbox 15A in relation to the gear ratioin the range gearbox 15B, the vehicle 1 may be driven in the reversedirection at a velocity, which is low enough to have control over thevehicle 1 even though a clutch 11 between the engine 4 and the gearbox 2is completely engaged. A crawler gear 211 in the main gearbox 15A is,according to the invention, engaged when a reverse gear is engaged inthe range gearbox 15B. The velocity of the vehicle 1 driven in thereverse direction at a gear with the gear ratio mentioned above and withthe clutch 11 completely engaged will be below three km/h.

According to FIG. 2, the main gearbox 15A alone can be set to fourdifferent gear ratios. The range gearbox 15B is arranged downstream ofthe main gearbox 15A. The range gearbox 15B is surrounded by a gearboxhousing 12 and is discussed further with reference to FIGS. 3-5. Thesplit gearbox 15C is located upstream of the main gearbox 15A in thedirection of the torque from the combustion engine 4 to drive the wheels8. The split gearbox 15C duplicates the number of gears of the maingearbox 15A in order to provide more gear ratios of the gearbox 2.

Instead of a disengageable clutch 11, first and second electricalmachines (not disclosed) may be arranged to rotate and brake a planetarygear 14 (not disclosed) arranged in the powertrain 3 and locatedupstream of the gearbox 2. In such an arrangement, the first electricalmachine may be arranged at a sun gear wheel (not disclosed) of theplanetary gear 14, and the second electrical machine may be arranged atthe first ring gear wheel (not disclosed) of the planetary gear 14. Thefirst and second electrical machines may be the power source or may formpart of the power source.

With regard to the main gearbox 15A, a layshaft 202 comprises gearwheels 203A, 204A, 205A that are rotatably fixed to the layshaft 202.For example, the gear wheel 203A represents the second gear, the gearwheel 204A represents the first gear, and the gear wheel 205A representsthe third gear. A mainshaft 206 comprises corresponding gear wheels203B, 204B, 205B, which rotate freely in relation to the mainshaft 206,but which can be selectively locked for rotation with the mainshaft 206in order to engage a gear. For example, the second main gearbox gear canbe engaged by manoeuvring a first main sleeve 207, arranged to rotatewith the mainshaft 206, to a position where the gear wheel 203B isengaged, i.e. to the left in the figure, thereby bringing the gear wheel203B to rotate the mainshaft 206 and to engage the layshaft 202 to themainshaft 206 via the gear wheel 203A. Each pair of the gear wheels onthe layshaft 202 and the mainshaft 206 represent a gear ratio.

The first main gearbox gear can be engaged by disengaging the first mainsleeve 207 from the gear wheel 203B and instead moving a second mainsleeve 208 to a position to the right in the figure where gear wheel204B is engaged, thereby bringing the gear wheel 204B to rotate themainshaft 206. Correspondingly, the third main gearbox gear can beengaged by manoeuvring the second main sleeve 208 to a position to theleft in the figure where a gear wheel 205B is engaged, thereby settingthe main gearbox 15A to third gear. Each of the first through thirdgears is used for a plurality of the total number of gears provided bythe gearbox 2 as a whole. For example, the first gear of the maingearbox 15A will be used for the first and the second gears of thegearbox 2, the low and the high split, the low range, and also for theseventh and the eighth gears, the low and the high split, and the highrange. The different gears in the split gearbox 15C and the main gearbox15A may also be used when the range gearbox 15B is shifted into thereverse gear.

The crawler gear 211 in the main gearbox 15A comprises a crawler gearwheel pair 211A and 211B. The crawler gear wheel 211A is arranged on thelayshaft 202 and the crawler gear wheel 211B may rotate freely inrelation to the mainshaft 206, but can be selectively locked forrotation with the mainshaft 206 in order to engage the crawler gear 211.

Further, with regard to the split gearbox 15C, the incoming gear 17comprises an incoming gear wheel 209A that, similar to the above, isrotatably fixed to the layshaft 202 and a corresponding incoming gearwheel 209B that rotates freely in relation to the input shaft 201 butwhich can be selectively locked for rotation with the input shaft 201through a split sleeve 210, which may be provided with a splitsynchronising unit. The split sleeve 210 can further be used to connectthe gearbox input shaft 201 to gear wheel 205B directly. The incominggear 17, which comprises the gear wheel pair 209A-B can together withthe split sleeve 210 thereby provide two different split gear ratios foreach gear of the main gearbox 15A into two parts.

When, for example, the first gear is engaged, the split sleeve 210 isarranged to engage the split gear wheel 205B. Consequently, the inputshaft 201 is directly connected to the split gear wheel 205B, which, viathe split gear wheel 205A, establishes a first gear ratio between theinput shaft 201 and the layshaft 202. The gear wheel 205B, however, isnot connected to the mainshaft 206, but the layshaft 202 is connected tothe mainshaft 206 through the gear wheel pair 204A-B and by means of thesecond main sleeve 208.

When the second gear is engaged (i.e. high split of the first maingearbox gear) the vehicle 1 is, instead, driven with the gear wheel pair209A-B engaged, resulting in a second gear ratio between an input shaft201 and the layshaft 202. The gear wheel 204B is still engaged by thesecond main sleeve 208 according to the above, thereby extending therange of each gear.

This split can be performed for each gear of the main gearbox 15A.However, when the coupling unit 210 engages gear wheel 205B and also thesecond main sleeve 208 engages the gear wheel 205B a gear ratio of 1:1through the split gearbox 15C and the main gearbox 15A is obtained.

The crawler gear 211 is, according to the invention, engaged when thereverse gear is engaged in the range gearbox 15B. A first reverse gearis engaged when also the split sleeve 210 is arranged to engage thesplit gear wheel 205B. This will have the result that the input shaft201 is directly connected to the split gear wheel 205B, which, via thesplit gear wheel 205A, establishes a gear ratio between the input shaft201 and the layshaft 202.

The crawler gear 211 in the main gearbox 15A is arranged to transfertorque through the gearbox 2 when the range gearbox 15B is shifted intothe reverse gear. Thus, when a reverse gear is engaged in the rangegearbox 15B, the crawler gear 211 is engaged. Due to the crawler gear211, the vehicle 1 may be driven in the reverse direction at a velocity,which is low enough for a driver of the vehicle 1 to have control overthe vehicle 1.

As an example, the gear ratio of the crawler gear is in the range3.1:1-3.9:1. When the gear ratio of the crawler gear 211 is in the range3.1:1-3.9:1, the vehicle 1 may be driven in the reverse direction at avelocity, which is low enough to have control over the vehicle 1. Thus,the driveability of the vehicle 1 in the reverse direction will beacceptable. The overall dimensions of the gearbox 2 can be reduced.Also, there is no need to increase the gear ratio of the planetary gear14 in the range gearbox 15B by minimizing the diameter of the sun gearwheel 18.

According to another example, the gear ratio of the crawler gear 211 isin the range 3.4:1-3.6:1. When the gear ratio of the crawler gear 211 isin the range 3.4:1-3.6:1, the vehicle 1 may be driven in the reversedirection at a velocity, which is low enough to have control over thevehicle 1. Thus, the driveability of the vehicle 1 in the reversedirection will be improved. The overall dimensions of the gearbox 2 canbe reduced further. Also, there is no need to increase the gear ratio ofthe planetary gear 14 in the range gearbox 15B by minimizing thediameter of the sun gear wheel 18.

The crawler gear 211 is only engaged when the gearbox 2 is shifted intothe reverse gear, and in the forward direction when the range gearbox15B is shifted into the low range position. In comparison to other gearsused when driving a vehicle 1 in the forward direction, such as the gearwheel pair 204A-B representing the first gear in the main gearbox 15A,the reverse gear is less used and also the crawler gear 211 in theforward direction is less used. Also, the torque transferred through thecrawler gear 211 is less than the torque transferred through the othergears in the gearbox 2, such as the gear wheel pair 204A-B, due to thehigh gear ratio in the crawler gear 211. For this reason, the wear ofthe crawler gear wheel pair 211A and 211B will be limited. Thus, thecrawler gear wheels 211A and 211B may be designed for bringing theoverall dimensions of the gearbox 2 to a minimum. The width wC of thecrawler gear wheel 211A arranged on the layshaft 202 and the width wC ofthe crawler gear wheel 211B arranged on the mainshaft 206 are smallerthan the width W1 of the gear wheel pair 204A-B representing the firstgear in the main gearbox 15A. Thus, the gear wheel pair 204A and 204B inthe main gearbox 15A have the second largest gear ratio after the gearratio of the crawler gear 211. In comparison to gears used when drivinga vehicle 1 in the forward direction, the reverse gear is less used. Thecrawler gear wheels 211A and 211B may thus be designed with a width wCthat is smaller than the width W1 of the gear wheel pair 204A-B, whichhave the second largest gear ratio in the main gearbox 15A, because thewear of the crawler gear wheels 211A and 211B may be less than the wearof the gear wheels 204A and 204B. The smaller width wC of the crawlergear wheels 211A and 211B will bring the length of the gearbox 2shorter.

According to FIG. 2, the crawler gear 211 is arranged in the maingearbox 15A. However, it may also be possible to arrange the crawlergear 211 in the split gearbox 15C, so that the crawler gear wheel 211Ais arranged on the input shaft 201 and the crawler gear wheel 211B isarranged on the layshaft 202.

According to a further aspect of the invention, the planetary gear 14 isarranged to have a gear ratio 3.1:1-3.9:1 when shifted into the reversegear. When the gear ratio of the planetary gear 14 is in the range3.1:1-3.9:1, the vehicle 1 may be driven in the reverse direction at avelocity, which is low enough to have control over the vehicle 1. Thus,the driveability of the vehicle 1 in the reverse direction will beacceptable. The overall dimensions of the gearbox 2 can be reduced.Also, there is no need to increase the gear ratio of the planetary gear15 in the range gearbox 15B by minimizing the diameter of the sun gearwheel 18.

According to a further aspect of the invention, the planetary gear 14 isarranged to have a gear ratio in the range 3.3:1-3.6:1 when shifted intothe reverse gear. When the gear ratio of the planetary gear 14 is in therange 3.3:1-3.6:1, the vehicle 1 may be driven in the reverse directionin a velocity, which is low enough to have control over the vehicle 1.Thus, the driveability of the vehicle 1 in the reverse direction may beimproved. The overall dimensions of the gearbox 2 may be reducedfurther. Also, there is no need to increase the gear ratio of theplanetary gear 14 in the range gearbox 15B by minimizing the diameter ofthe sun gear wheel 18.

The two highest gears in the low range gear position and the two lowestgears in a high range gear position may be overlapping. Thus, the twohighest gears in the low range gear positions may have substantially thesame gear ratio as the two lowest gears in a high range gear position.However, at least the highest gear in the low range gear position and atleast the lowest gear in a high range gear position should beoverlapping. Thus, at least the highest gear in the low range gearpositions should have substantially the same gear ratio as at least thelowest gear in a high range gear position. This overlapping gear ratiowill increase the total gear ratio in the gearbox 2. This will bring theoverall components in the gearbox 2 to a minimum and also utilize all ofthe transmission components effectively.

The split gearbox 15C comprises an incoming gear 17 and a split gear 19.The gear ratio of the split gear 19 may be larger than the gear ratio ofthe incoming gear 17, so that the overall gear ratio in the gearbox 2may be increased. As an example, the gear ratio of the incoming gear 17may be in the range 0.9:1-1.1:1 and thus the gear ratio of the splitgear 19 may be larger than 0.9:1-1.1:1. When the gear ratio of theincoming gear 17 is in the range 0.9:1-1.1:1, the overall gear ratio ofthe gearbox 2 may be increased and the vehicle 1 may be driven in thereverse direction at a velocity that is low enough for a driver of thevehicle 1 to have control over the vehicle 1. Thus, the driveability ofthe vehicle 1 in the reverse direction will be acceptable. The overalldimensions of the gearbox 2 can be reduced. Also, there is no need toincrease the gear ratio of the planetary gear 14 in the range gearbox15B by minimizing the diameter of the sun gear wheel 18.

According to another example, the gear ratio of the incoming gear 17 maybe in the range 0.95:1-1.05:1 and thus the gear ratio of the split gear19 may be larger than 0.95:1-1.05:1. When the gear ratio of the incominggear 17 is in the range 0.95:1-1.05:1, the overall gear ratio of thegearbox 2 may be increased and the vehicle 1 may be driven in thereverse direction at a velocity, which is low enough for a driver of thevehicle 1 to have control over the vehicle 1. Thus, the driveability ofthe vehicle 1 in the reverse direction may be improved. The overalldimensions of the gearbox 2 can be reduced further. Also, there is noneed to increase the gear ratio of the planetary gear 14 in the rangegearbox 15B by minimizing the diameter of the sun gear wheel 18.

The gear ratio of the incoming gear 17 may also be substantially 1:1 andthus the gear ratio of the split gear 19 may be larger than 1:1. Whenthe gear ratio of the incoming gear 17 is substantially 1:1, the overallgear ratio of the gearbox 2 may be increased and the vehicle 1 may bedriven in the reverse direction at a velocity, which is low enough for adriver of the vehicle 1 to have control over the vehicle 1. Thus, thedriveability of the vehicle 1 in the reverse direction will be verygood. The overall dimensions of the gearbox 2 can be reduced evenfurther. Also, there is no need to increase the gear ratio of theplanetary gear 14 in the range gearbox 15B by minimizing the diameter ofthe sun gear wheel 18.

The split gearbox 15C and the main gearbox 15A may together be arrangedto have a combined ratio spread in the range 5.5-6.3 and the planetarygear 14 is arranged to have a gear ratio in the range 3.1:1-3.9:1 whenshifted into the reverse gear. With such a combined ratio spread in thesplit gearbox 15C and the main gearbox 15A together with such a gearratio in the range gearbox 15B, the vehicle 1 may be driven in thereverse direction at a velocity, which is low enough for a driver of thevehicle 1 to have control over the vehicle 1. Thus, the driveability ofthe vehicle 1 in the reverse direction will be acceptable. The overalldimensions of the gearbox 2 can be reduced. Also, there is no need toincrease the gear ratio of the planetary gear 14 in the range gearbox15B by minimizing the diameter of the sun gear wheel 18. The definitionof the ratio spread is the largest combined or common gear ratio of thesplit gearbox 15C and the main gearbox 15A divided with the minimumcombined or common gear ratio of the split gearbox 15C and the maingearbox 15A.

As an alternative, the split gearbox 15C and the main gearbox 15A maytogether be arranged to have a combined ratio spread in the range5.7-6.1 and the planetary gear 14 is arranged to have a gear ratio inthe range 3.3:1-3.6:1 when shifted into the reverse gear. With such acombined ratio spread in the split gearbox 15C and the main gearbox 15Atogether with such a gear ratio in the range gearbox 15B, the vehicle 1may be driven in the reverse direction at a velocity, which is lowenough for a driver of the vehicle 1 to have control over the vehicle 1.Thus, the driveability of the vehicle 1 in the reverse direction will beimproved. The overall dimensions of the gearbox 2 can be reducedfurther. Also, there is no need to increase the gear ratio of theplanetary gear 14 in the range gearbox 15B by minimizing the diameter ofthe sun gear wheel 18.

From above, it is evident that the split gearbox 15C and the maingearbox 15A are together arranged to have a highest gear ratio, which islarger than the gear ratio of the planetary gear 14 in the range gearbox15B when shifted into the reverse gear. Consequently, the split gearbox15C and the main gearbox 15A together will have a large combined ratiospread, which in total will be over 5.

FIG. 3 shows a schematic sectional view of a gearbox 2 of the presentinvention. The gearbox 2 comprises a main gearbox 15A, a split gearbox15C and the range gearbox 15B. The range gearbox 15B comprises aplanetary gear 14, which has a low and a high gear, so that theswitching capability of the gearbox 2 can be divided into a low rangegear position and a high range gear position. In a first gear positioncorresponding to the low range gear position, a downshift takes place inthe planetary gear 14. In the high range gear position, the gear ratiois 1:1 in the planetary gear 14. The planetary gear 14 in FIG. 3 isshifted into the first gear position, corresponding to the low rangegear position.

The range gearbox 15B is accommodated in the gearbox housing 12 andcomprises a range gearbox input shaft 16 that may be a mainshaft 26 ofthe main gearbox 15A. The planetary gear 14 comprises three maincomponents, which are rotatably arranged in relation to each other,namely a sun gear wheel 18, a planet carrier 20 and a ring gear wheel22. A number of planet gear wheels 24 are rotatably arranged withbearings on the planet carrier 20. With knowledge of the number of teeth32 of the sun gear wheel 18 and the ring gear wheel 22, the relativegear ratio of the three components can be determined. The sun gear wheel18 is rotatably connected to the input shaft 16 and the planet gearwheels 24 engage the sun gear wheel 18. The ring gear wheel 22 surroundsand engages the planet gear wheels 24.

A first axially displaceable coupling sleeve 42 is, in a first gearposition, arranged to connect, the transmission case 12 with the ringgear wheel 22 and, in a second gear position, arranged to disconnect thetransmission case 12 from the ring gear wheel 22. The first axiallymovable coupling sleeve 42 is, in the first gear position, arranged todisconnect the input shaft 16 from the planet carrier 20.

A second axially displaceable coupling sleeve 43 is in a third gearposition arranged to couple the ring gear wheel 22 with an output shaft28 of the gearbox 2. The output shaft 28 is coupled to the propellershaft 10 of the vehicle 1. In the third gear position, corresponding toa reverse gear, the first axially displaceable coupling sleeve 42 isarranged to disconnect the input shaft 16 from the planet carrier 20 andto interconnect the planet carrier 20 with the gearbox housing 12. Inthe first and second gear positions the second axially displaceablecoupling sleeve 43 is arranged to interconnect the planet carrier 20with the output shaft 28.

The first axially displaceable coupling sleeve 42 is on an inner surfaceprovided with first splines 50 arranged to interact with thecorresponding first splines 50 on the ring gear wheel 22 and on theperiphery of a projection 52, which is fixedly connected to thetransmission housing 12. The first splines 50 on the first axiallydisplaceable coupling sleeve 42 are also arranged to cooperate withcorresponding first splines 50 on the input shaft 16. Correspondingfirst splines 50 disposed on the input shaft 16 are formed on theperiphery of a first sprocket 46, which is mounted on a shaft 38 for thesun gear wheel 18. The first splines 50 on the first axiallydisplaceable coupling sleeve 42 are also arranged to cooperate withcorresponding first splines 50 on the planet carrier 20. Correspondingfirst splines 50 disposed on the planet carrier 20 are formed on theperiphery of a second sprocket 44, which is mounted on the planetcarrier 20.

The second axially displaceable coupling sleeve 43 is on an innersurface provided with second splines 51, which are arranged to cooperatewith corresponding second splines 51 on the ring gear wheel 22, theplanet carrier 20 and the output shaft 28. The corresponding secondsplines 51 arranged on the planet carrier 20 are formed on the peripheryof a third sprocket 49, which is mounted on the planet carrier 20. Thecorresponding second splines 51 provided on the output shaft 28 areformed on the periphery of a fourth sprocket 53, which is mounted on theoutput shaft 28.

The low gear in the gearbox 2 is obtained by displacing the firstcoupling sleeve 42, so that the ring gear wheel 22 is connected to thegearbox housing 12. The axial displacement of the first and the secondcoupling sleeves 42, 43 are provided with a first and second shift forks60, 61 arranged in an outside circumferential groove 62 in therespective coupling sleeves 42, 43. The first shift fork 60 isinfluenced by a first power means 66 and the second shift fork 61 isinfluenced by a second power means 67. The first and second power means66, 67 may be pneumatic or hydraulic cylinders. The shift forks 60, 61and power means 66, 67 are schematically shown in FIG. 3.

Preferably, the coupling sleeves 42, 43 each has a low weight, whichmeans that low energy and force are needed to move the respectivecoupling sleeves 42, 43 when shifting gears. This allows a quick gearshifting between the different gear positions in the gearbox 2.

FIG. 4 shows a schematic sectional view of the range gearbox 15B in thesecond gear position or the high range gear position in which the firstcoupling sleeve 42 is shifted to the right in FIG. 4 for connecting theinput shaft 16 to the planet carrier 20. The first coupling sleeve 42has in this position disconnected the ring gear wheel 22 of the gearboxhousing 12. The transmission of torque from the input shaft 16 to theoutput shaft 28 is in the high range gear position via the input shaft16 and the planet carrier 20 and further to the output shaft 28 via thesecond coupling sleeve 43, so that the gear ratio through the planetarygear 14 becomes 1:1. As an alternative, the second axially movablecoupling sleeve 43 may in the second gear position be arranged to engagethe ring gear wheel 22 with the output shaft 28.

In FIG. 5, the range gearbox 15B has been shifted into the third gearposition, which is the reverse gear. The second axially displaceablesleeve 43 is in the third gear position arranged to connect the ringgear wheel 22 with the output shaft 28. Thus, the second coupling sleeve43 is shifted by the second shift fork 61, so that the ring gear wheel22 is connected to the output shaft 28. The first coupling sleeve 42 isshifted by the first shift fork 60 to couple the planet carrier 20 withthe gearbox housing 12. The planet carrier 20 is provided with a secondsprocket 44 arranged for connecting the planet carrier 20 with thegearbox housing 12 by means of the first coupling sleeve 42. Thedisplacement of the respective clutch sleeve 42, 43 is performed whenthe input and the output shaft 16, 28 are stationary, which correspondsto a stationary operating state of the vehicle 1, when the range gearbox15B is included in the transmission 3 of a vehicle 1. In order toprovide a stationary position of the input shaft 16, the clutch 11 ofthe vehicle 1 is transferred to a disconnected mode. When the rangegearbox 15B is operated in the third gear position, the torque istransmitted from the input shaft 16 to the sun gear wheel 18 and furtherto the planet gear wheels 24, which transmits the torque to the ringgear wheel 22 and further to the output shaft 28 via the second couplingsleeve 43. The planet carrier 20 is stationary as the first couplingsleeve 42 connects the planet carrier 20 with the gearbox housing 12.

With the gear ratio mentioned above, the range gearbox 15B may have alimited diameter and still the driveability of the vehicle 1 in thereverse direction is not adversely affected. A limited diameter of therange gearbox 15B will bring the overall components in the gearbox 2 toa minimum, and thus manufacturing and repair costs will be saved. Thesun gear wheel 18 in the planetary gear 14 may be provided with adiameter, which withstands the considerable amount of torque needed.Thus, there is no need to increase the gear ratio of the planetary gear14 in the range gearbox 15B by minimizing the diameter of the sun gearwheel 18.

An electronic control unit 70 is coupled to the powertrain 3 to achievethe gear shifting above. A number of (not shown) speed sensors in thepowertrain 3 may be connected to the control unit 70. Another computer72 may also be connected to the control unit 70. The control unit 70 maybe a computer with appropriate software for this purpose. The controlunit 70 and/or the computer 72 comprise a computer program P, which caninclude routines to control the gearbox 2 of the present invention. Theprogram P may be stored in an executable form or compressed form in amemory M and/or in a read/write memory. Preferably, there is provided acomputer program product comprising a program code stored on a computerreadable medium for performing the gear shifting above, when the programis run on the control unit 70 or another computer 72 connected to thecontrol unit 70. The code may be stored in the computer readable mediumin a non-volatile manner.

The components and features specified above may within the framework ofthe invention be combined between the different embodiments specified.

The invention claimed is:
 1. A gearbox for a vehicle, the gearboxcomprising: a split gearbox, a main gearbox and a range gearbox, whichis shiftable into a low range gear position and a high range gearposition; the range gearbox comprises: a planetary gear with a ring gearwheel, a sun gear wheel and a planet carrier, on which at least oneplanet gear wheel is rotatably mounted, the ring gear wheel and sun gearwheel engage with the at least one planet gear wheel; a gearbox housingsurrounding the planetary gear; a first axially movable coupling sleevearranged to engage the planet carrier with the gearbox housing; and asecond axially movable coupling sleeve arranged to engage the ring gearwheel with an output shaft to shift into a reverse gear in the gearbox,wherein a crawler gear in the main gearbox is arranged to transfertorque through the gearbox when the range gearbox is shifted into thereverse gear so as to make the vehicle drive in a reverse direction. 2.The gearbox according to claim 1, wherein the gear ratio of the crawlergear is in the range 3.1:1-3.9:1.
 3. The gearbox according to claim 1,wherein the gear ratio of the crawler gear is in the range 3.4:1-3.6:1.4. The gearbox according to claim 1, wherein the crawler gear is onlyengaged when the gearbox is shifted into the reverse gear and in theforward direction when the range gearbox is shifted into the low rangeposition.
 5. The gearbox according to claim 1, wherein the planetarygear is arranged to have a gear ratio in the range 3.1:1-3.9:1 whenshifted into the reverse gear.
 6. The gearbox according to claim 1,wherein the planetary gear is arranged to have a gear ratio in the range3.3:1-3.7:1 when shifted into the reverse gear.
 7. The gearbox accordingto claim 1, wherein the split gearbox and the main gearbox are togetherarranged to have a largest combined gear ratio which is larger than thegear ratio in the planetary gear in the range gearbox when shifted intothe reverse gear.
 8. The gearbox according to claim 1, wherein the widthof a crawler gear wheel of the crawler gear is smaller than the width ofa gear wheel in a gear in the main gearbox having the second largestgear ratio.
 9. The gearbox according to claim 8, wherein one crawlergear wheel of the crawler gear is arranged on a mainshaft in the maingearbox and the another crawler gear wheel of the crawler gear isarranged on a layshaft.
 10. The gearbox according to claim 8, whereinone crawler gear wheel of the crawler gear is arranged on an input shaftin the split gearbox and the another crawler gear wheel of the crawlergear is arranged on a layshaft.
 11. The gearbox according to claim 1,wherein the gearbox is arranged to have an overlapping gear ratio in atleast the highest gear in the low range gear position and at least thelowest gear in a high range gear position.
 12. The gearbox according toclaim 11, wherein the gearbox is arranged to have an overlapping gearratio in the two highest gears in the low range gear position and thetwo lowest gears in a high range gear position.
 13. A vehicle, whereinthe vehicle is provided with a gearbox according to claim 1.